In the related art, a lavatory pan washing apparatus in which washing water is supplied into a water sealing portion composed of a lower portion of a lavatory bowl and a rising conduit continuing thereto and air is sucked from a water discharge channel continuing to a downstream side of the water sealing portion for causing siphon action in a lavatory pan is proposed (Japanese Patent Application Publication No. JP-A-H10-96255). The lavatory pan washing apparatus as an example in the aforementioned Publication NO. JP-A-H10-96255 includes an ejector (referred to as “aspirator” in the aforementioned Publication No. JP-A-H10-96255) provided at a midway of a water supply pipe for discharging water to a rim water channel of the lavatory pan and a switch valve provided on a water supply pipe on the downstream side of the ejector. A pipe continuing to the water discharge channel is connected to an inlet port of the ejector, and the switch valve is also positioned at a midway of the pipe.
When washing the lavatory pan by the lavatory pan washing apparatus, supply of washing water to the rim water channel is started first while supplying washing water to the ejector. Then, the switch valve is switched right after to communicate the inlet port of the ejector to the water discharge channel. Accordingly, the ejector sucks air from the water discharge channel by a negative pressure generated at the inlet port. Therefore, the siphon action takes place.
A laboratory pan washing apparatus disclosed in Japanese Patent Application Publication No. JP-A-2002-61262 is also proposed. The lavatory pan washing apparatus as an example in the aforementioned Publication No. JP-A-2002-61262 includes a water supply pipe for supplying washing water branched into a pipe for discharging water to a rim water channel and a pipe to be connected to the ejector (referred to as “jet pump” in the aforementioned Publication No. JP-A-2002-61262), and an air inlet port of the ejector is connected to a water discharge channel.
When washing the lavatory pan by this lavatory pan washing apparatus, supply of washing water to the ejector is started at the same time as start of supply of washing water to the rim water channel. Accordingly, the ejector sucks air from the water discharge channel by a negative pressure generated at an inlet port. Therefore, the siphon action takes place.
However, in the lavatory pan washing apparatuses disclosed in the aforementioned Japanese patent application publications, air is sucked from the water discharge channel to cause the siphon action immediately after or simultaneously with starting of supply of washing water to the rim water channel of the lavatory pan. In other words, in these lavatory pan washing apparatuses, air in the water discharge channel is sucked to cause the siphon action in a state in which very little amount of washing water is supplied to the lavatory bowl of the lavatory pan or in a state in which no washing water is supplied thereto. In this case, since the potential energy and the kinetic energy of washing water stored in the lavatory bowl are small, water force to the water discharge channel is weak, and hence sewage or the like in the lavatory bowl cannot be discharged sufficiently. When the amount of supply of washing water from the rim water channel to the lavatory bowl is small, the sewage or paper in the lavatory bowl cannot be dashed with the washing water, and hence sufficient discharge of the sewage or the like in the lavatory bowl cannot be achieved from this point as well.
On the other hand, in this lavatory pan washing apparatus, increasing the force of washing water supplied from the rim water channel to the lavatory bowl is considered for achieving sufficient discharge of the sewage in the lavatory bowl. However, in order to do so, it is necessary to increase the amount of supply of washing water, which contradicts the idea of water saving.